ISO 128000 with no noise eh . . . let's see about the math behind that *ist D has 3008x2008 pixels on a 23.5mm x 15.7mm sensor - that's a pixel pitch (d) of about 7.8 microns
*istD has acceptable noise at ISO 1600 *Signal to noise ratio (S/N) must remain constant for equal quality. *Signal strength (the number of electrons on the CCD) (S) is proportional to the area of a sensor at a given ISO. doubling ISO cuts signal strength by half. There S ~ d*d/ISO *Thermal noise is a random function caused by electrons jumping the silicon band gap at the photosite. Statistical methods can be used to show that the standard deviation of the noise component is proportional to d (N~d) *S/N ~ (d*d/(ISO)/d) ~ d/ISO *so to double iso without changing S/N, you need to double the pixel pitch d. for ISO 128000, d = 128000*7.8 microns/1600 = 624 microns. *At the same size as the *ist D, you get a sensor which is 38 pixels by 25 pixels - 950 pixel total. Ouch! There are remarkably few places to gain ground. A higher percentage of the sensor area can be used for photosites. Quantum efficiency of sensors can be improved to boost S. A different semiconductor with a larger band gap could be used to reduce noise, but this is unlikely since silicon is already well suited to detecting visible light. You could put a cooling device on the CCD to reduce noise, and that's about all. -Scott On Wed, 2004-06-09 at 19:01, Rob Studdert wrote: > On 9 Jun 2004 at 18:52, Alan Chan wrote: > > > I think the "IS" alone for telephotos is a good enough reason to switch, if one > > needs it. Nothing else matter if the images were blurred due to slow shutter > > speed. I often found myself struggling with 1/60s even with ISO400 film when > > using 200/2.8 & 300/4.5 w/o tripod. I wonder why I am still with Pentax > > sometimes. :-) > > I generally have far more problems with subject movement than I do with camera > shake, I don't need IS I need ISO 128000 with no noise. > > > Rob Studdert > HURSTVILLE AUSTRALIA > Tel +61-2-9554-4110 > UTC(GMT) +10 Hours > [EMAIL PROTECTED] > http://members.ozemail.com.au/~distudio/publications/ > Pentax user since 1986, PDMLer since 1998
